Chatter or instability in machining operations, such as turning, boring, milling and the like, is a common problem in industry. Production time, which is related in large part to the rate of metal removal in machining, is usually restricted by the dynamic characteristics of the machine tool and the workpiece, and these characteristics can vary depending upon the operating conditions of the machine tool, such as rotational speed, feed rate, temperature and others, and by geometry of the workpiece and the relative orientation and velocity of the chip removal tools relative to the workpiece. These dynamic characteristics, in turn, limit the stability of the machine tool and, hence, restrict its production capacity. Further, such instability may cause tool failure, with potentially serious damage to the workpiece, and may significantly reduce production rates due to necessary time needed for corrective action.
When seeking to control this chatter or instability, it has been found that it is not always possible to eliminate fully the instability by properly designing the machine tool. The geometry of the workpiece may dictate elements of the machine tool configuration that promote instability. Additionally, the workpiece may, by its very nature, be a source of instability in a given machining process.
Over the years several techniques to reduce chatter have been attempted. However, such prior art efforts have generally been unsatisfactory for a variety of reasons. One prior art technique for chatter elimination was published by Weck and Gather but was restricted to face milling operations and required extensive prior knowledge of the dynamic characteristics of the machine tool, which characteristics must then be quantified or measured prior to the use of the machine tool. Other systems described by Takemura and Hoshi have addressed the problem of chatter by periodically varying speed of rotation. However, this technique of continuous periodic speed variation requires substantial modifications to the machine tool drive and was limited, in any event, to lathe operations.